U.S. patent application number 09/865478 was filed with the patent office on 2002-12-12 for solid composite polymer electrolyte.
This patent application is currently assigned to Chung Yuan Christian University. Invention is credited to Chen, Hung-Chang, Chen-Yang, Yui-Whei, Lin, Fu-Luo.
Application Number | 20020185627 09/865478 |
Document ID | / |
Family ID | 25345599 |
Filed Date | 2002-12-12 |
United States Patent
Application |
20020185627 |
Kind Code |
A1 |
Chen-Yang, Yui-Whei ; et
al. |
December 12, 2002 |
Solid composite polymer electrolyte
Abstract
A solid composite polymer electrolyte contains a general
amorphous branched polymer having recurrent units, each of which
includes a backbone chain and at least a side chain linked to the
backbone chain and containing at least one coordination potential
atom, an amphoteric metal salt dispersed in the branched polymer
and forming Lewis acid-base interactions with the side chains, and
an amphoteric Lewis acid-base ceramic filler dispersed in the
branched polymer and forming Lewis acid-base interactions with the
side chains and the metal salt.
Inventors: |
Chen-Yang, Yui-Whei;
(Hsinchu, TW) ; Chen, Hung-Chang; (Chiayi Hsien,
TW) ; Lin, Fu-Luo; (Taichung Hsien, TW) |
Correspondence
Address: |
MORGAN, LEWIS & BOCKIUS LLP
1800 M Street, N. W.
Washington
DC
20036-5869
US
|
Assignee: |
Chung Yuan Christian
University
|
Family ID: |
25345599 |
Appl. No.: |
09/865478 |
Filed: |
May 29, 2001 |
Current U.S.
Class: |
252/62.2 ;
429/306; 429/323 |
Current CPC
Class: |
H01M 10/0565 20130101;
H01B 1/122 20130101; Y02E 60/10 20130101; H01M 2300/0091 20130101;
H01M 6/181 20130101; H01M 10/052 20130101; H01M 6/188 20130101 |
Class at
Publication: |
252/62.2 ;
429/306; 429/323 |
International
Class: |
H01G 002/00; H01M
006/18 |
Claims
We claim:
1. A solid composite polymer electrolyte comprising: a general
amorphous branched polymer having recurrent units, each of which
includes a backbone chain and at least a side chain linked to said
backbone chain and containing at least one coordination potential
atom; an amphoteric metal salt dispersed in said branched polymer
and forming Lewis acid-base interactions with said side chains; and
an amphoteric Lewis acid-base ceramic filler dispersed in said
branched polymer and forming Lewis acid-base interactions with said
side chains and said metal salt.
2. The solid composite polymer electrolyte of claim 1, wherein said
backbone chain of said branched polymer is selected from a group
consisting of a --P.dbd.N-- group and a --C--C-- group, and said
coordination potential atom of said side chain is selected from a
group consisting of an alkoxy group and a C.ident.N group.
3. The solid composite polymer electrolyte of claim 2, wherein said
backbone chain of said branched polymer is a --P.dbd.N-- group, and
said coordination potential atom of said side chain is an alkoxy
group.
4. The solid composite polymer electrolyte of claim 3, wherein said
branched polymer is poly[bis(methoxy ethoxyethoxy)phosphazene]
having a molecular weight ranging from about 1000 to about
10.sup.6.
5. The solid composite polymer electrolyte of claim 2, wherein said
backbone chain of said branched polymer is a --C--C-- group, and
said coordination potential atom of said side chain is a C.ident.N
group.
6. The solid composite polymer electrolyte of claim 5, wherein said
branched polymer is polyacrylonitrile having a molecular weight
ranging from about 10000 to about 10.sup.7.
7. The solid composite polymer electrolyte of claim 2, wherein said
ceramic filler is made from a material selected from a group
consisting of .alpha.-Al.sub.2O.sub.3 and TiO.sub.2.
8. The solid composite polymer electrolyte of claim 7, wherein said
metal salt is a lithium salt.
9. The solid composite polymer electrolyte of claim 8, wherein said
lithium salt is lithium perchlorate.
10. The solid composite polymer electrolyte of claim 9, wherein
said branched polymer is poly[bis(methoxy
ethoxyethoxy)phosphazene], and said ceramic filler is made from
.alpha.-Al.sub.2O.sub.3, said solid composite polymer electrolyte
comprising 86 to 95% by weight of poly[bis(methoxy
ethoxyethoxy)phosphazene], 4 to 9% by weight of lithium
perchlorate, and 1 to 5% by weight of .alpha.-Al.sub.2O.sub.3.
11. The solid composite polymer electrolyte of claim 10, comprising
90 to 92.5% by weight of poly[bis(methoxy
ethoxyethoxy)phosphazene], 5.5 to 7% by weight of lithium
perchlorate, and 2 to 3% by weight of .alpha.-Al.sub.2O.sub.3.
12. The solid composite polymer electrolyte of claim 9, wherein
said branched polymer is polyacrylonitrile, said solid composite
polymer electrolyte comprising 41 to 70% by weight of
polyacrylonitrile, 27 to 50% by weight of lithium perchlorate, and
3 to 9% by weight of said ceramic filler.
13. The solid composite polymer electrolyte of claim 12, comprising
47 to 60% by weight of polyacrylonitrile, 35 to 45% by weight of
lithium perchlorate, and 5 to 8% by weight of said ceramic
filler.
14. The solid composite polymer electrolyte of claim 7, wherein
said ceramic filler has a particle size less than 150 microns.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a solid composite polymer
electrolyte, more particularly to a solid composite polymer
electrolyte having a branched polymer that has recurrent units,
each of which includes a backbone chain and at least a side chain
which is linked to the backbone chain and which contains at least
one coordination potential atom.
[0003] 2. Description of the Related Art
[0004] Since the early 1970s, polymer electrolytes has attracted
many researchers due to the possibility of its application to
various electrochemical devices, such as batteries, electrochromic
windows, displays and fuel cells. Many polymeric electrolytes have
been reported and they may be divided into three categories, dry
solid type, gel-type and composite type. The dry solid type polymer
electrolytes presently show lower ionic conductivity
(.about.10.sup.-5 Scm.sup.-1 at room temperature) but are less
harmful to the environment. While the gel-type polymer electrolytes
have higher ionic conductivities (.about.10.sup.-3 Scm.sup.-1 at
room temperature), they are hazardous due to the incorporated
organic solvent. The composite type, a subset of the solid
electrolytes, is usually called composite polymer electrolytes. Due
to the presence of ceramic fillers, such as Al.sub.2O.sub.3,
TiO.sub.2 etc., the composite polymer electrolytes usually show a
higher ionic conductivity, a better mechanical property, and
electrolyte-metal electrode interfacial stability.
[0005] During the past years, most research on composite polymer
electrolytes have focused on polyether-based matrices, especially
on polyether oxide (PEO) composite electrolytes. The effect of
ceramic fillers and salt concentration on the conductivity,
transport number and electrode-electrolyte interfacial interaction
of PEO-based composite electrolytes has been investigated and
reviewed. The conductivity enhancement by addition of the ceramic
fillers has been attributed mainly to the decreased crystallinity
of the PEO-based polymer matrix.
[0006] On the other hand, the poly[bis(methoxyethoxy
ethoxy)phosphazene] (MEEP)/lithium salt electrolytes system showed
higher conductivity (1.7.times.10.sup.-5 Scm.sup.-1at room
temperature) than the corresponding PEO-lithium salt electrolyte
system (.about.10.sup.-8 Scm.sup.-1 at 20.degree. C.). However,
poor mechanical stability is a shortcoming for practical
application. Therefore, many efforts, which include the
cross-linking of MEEP, the chemical cross-linking of MEEP with
poly(ethylene glycol), the Co .alpha. irradiation of ether MEEP or
MEEP-(LiX).sub.0.25 complexes, or the use of a porous, fiberglass
matrix to support MEEP have been proposed to solve this problem.
The best conductivities of these electrolyte systems are in the
range of 1.0.times.10.sup.-5 to 7.0.times.10.sup.-5 Scm.sup.-1 at
room temperature. Nevertheless, an increase in mechanical stability
is usually paid off by a decrease in conductivity.
[0007] Recently, there has been proposed structured polymer
electrolytes that can lead to enhanced ionic conductivity. However,
the enhancement is still limited.
[0008] Accordingly, the conduction mechanism in polymer
electrolytes is relatively complex, and there remains a need for
the improvement of the conductivity of the polymer electrolyte.
SUMMARY OF THE INVENTION
[0009] Therefore, it is an object of the present invention to
provide a solid composite polymer electrolyte with good mechanical
property and high conductivity at room temperature.
[0010] Accordingly, the solid composite polymer electrolyte of the
present invention comprises: a general amorphous branched polymer
having recurrent units, each of which includes a backbone chain and
at least a side chain linked to the backbone chain, the side chain
containing at least one coordination potential atom; an amphoteric
metal salt dispersed in the branched polymer and in Lewis acid-base
interaction with the side chains; and an amphoteric Lewis acid-base
ceramic filler dispersed in the branched polymer and forming Lewis
acid-base interaction with the side chains and the metal salt.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] The inventors have found that, in contrast with the teaching
of the aforesaid reduction of the crystallinity of the PEO-based
polymer matrix by the addition of ceramic fillers, the conductivity
of the polymer electrolyte can be significantly enhanced when the
polymer electrolyte contains a general amorphous branched polymer
having recurrent units, each of which includes a backbone chain and
at least a side chain linked to the backbone chain and containing
at least one coordination potential atom, an amphoteric metal salt
dispersed in the branched polymer and forming Lewis acid-base
interactions with the side chains, and an amphoteric Lewis
acid-base ceramic filler dispersed in the branched polymer and
forming Lewis acid-base interactions with the side chains and the
metal salt. The aforesaid general amorphous branched polymer is
defined herein as a branched polymer that is completely amorphous
or that can be considered as amorphous with partially
microcrystalline domains.
[0012] For the ceramic-free polymer electrolyte, there is only one
Lewis acid-base interaction between the metal ion of the metal salt
and the coordination potential atom. On the other hand, for the
ceramic-containing polymer electrolyte, there are three Lewis
acid-base interactions among the metal ion of the metal salt, the
coordination potential atom, and the ceramic filler. As a
consequence, the addition of the ceramic filler provides extra
paths for the metal ion transport in the polymer electrolyte, and
thus greatly enhances the conductivity of the polymer electrolyte.
Moreover, the enhancement of the conductivity is extended over a
larger concentration range for the ceramic-containing polymer
electrolyte than that for the ceramic-free polymer electrolyte.
[0013] In a preferred embodiment, the backbone chain of the
branched polymer is selected from a group consisting of a
--P.dbd.N-- group and a --C--C-- group, whereas the coordination
potential atom of the side chain is selected from a group
consisting of an alkoxy group and a C.ident.N group. Preferably,
when the backbone chain of the branched polymer is a --P.dbd.N--
group, the side chain is an alkoxy group, and when the backbone
chain of the branched polymer is a --C--C-- group, the side chain
is a C.ident.N group. More preferably, the branched polymer is
selected from a group consisitng of poly[bis(methoxy
ethoxyethoxy)phosphazene] and polyacrylonitrile.
[0014] Preferably, the ceramic filler is made from a material
selected from a group consisting of .alpha.-Al.sub.2O.sub.3,
TiO.sub.2, SiO.sub.2, MgO, and BaTiO.sub.3.
[0015] Preferably, the metal salt is a lithium salt selected from a
group consisting of lithium perchlorate, LiI, LiCF.sub.3SO.sub.3,
LiN(CF.sub.3SO.sub.3).sub.2, and LiPF.sub.6.
[0016] In another preferred embodiment, the branched polymer is
poly[bis(methoxy ethoxyethoxy)phosphazene] having a molecular
weight ranging from about 1000 to about 10.sup.6, the ceramic
filler is made from .alpha.-Al.sub.2O.sub.3, and the solid
composite polymer electrolyte comprises 86 to 95% by weight of
poly[bis(methoxy ethoxyethoxy)phosphazen- e], 4 to 9% by weight of
lithium perchlorate, and 1 to 5% by weight of
.alpha.-Al.sub.2O.sub.3, preferably, 90 to 92.5% by weight of
poly[bis(methoxy ethoxyethoxy)phosphazene], 5.5 to 7% by weight of
lithium perchlorate (LiClO.sub.4), and 2 to 3% by weight of
.alpha.-Al.sub.2O.sub.3. When the weight of .alpha.-Al.sub.2O.sub.3
is lower than 1 wt %, the conductivity enhancement is relatively
poor, and when the weight is greater than 5 wt %, formation of
aggregates of the .alpha.-Al.sub.2O.sub.3 occurs, thereby greatly
reducing the conductivity.
[0017] In yet another preferred embodiment, the branched polymer is
polyacrylonitrile (PAN) having a molecular weight ranging from
about 10000 to about 10.sup.7, and the solid composite polymer
electrolyte comprises 41 to 70% by weight of polyacrylonitrile, 27
to 50% by weight of lithium perchlorate, and 3 to 9% by weight of
the ceramic filler, preferably, 47 to 60% by weight of
polyacrylonitrile, 35 to 45% by weight of lithium perchlorate, and
5 to 8% by weight of the ceramic filler. For the
PAN/LiO.sub.4/.alpha.-Al.sub.2O.sub.3 electrolyte system, when the
weight of .alpha.-Al.sub.2O.sub.3 is lower than 3 wt %, the
conductivity enhancement is relatively poor, and when the weight is
greater than 9 wt %, formation of aggregates of the
.alpha.-Al.sub.2O.sub.3 particles occurs, thereby greatly reducing
the conductivity. For the PAN/LiO.sub.4/TiO.sub.2 electrolyte
system, when the weight of TiO.sub.2 is lower than 3 wt %, the
conductivity enhancement is relatively poor, and when the weight is
greater than 9 wt %, formation of aggregates of the TiO.sub.2
particles occurs, thereby greatly reducing the conductivity.
[0018] Preferably, the PAN-based solid composite polymer
electrolyte further comprises a residual solvent which can enhance
extentability of the solid composite polymer electrolyte. The
solvent is selected from a group consisting of DMF
(dimethylformamide), ethylene carbonate (EC), propylene carbonate
(PC), and the like.
[0019] Preferably, the ceramic filler employed in the composite
polymer electrolyte of this invention has a particle size less than
150 microns.
[0020] Having the general nature of the invention set forth above,
the following Examples and Comparative Examples are presented in
order that the invention may be more readily understood.
EXAMPLES 1 to 18 AND COMPARATIVE EXAMPLES 1 to 6
[0021] A. Materials
[0022] Hexachlorocyclotriphosphazene was obtained from the Nippon
Fine Chemical Corp, Japan. Methoxyethoxyethanol was purchased from
Merck Chemical Co. Lithium perchlorate (LiClO.sub.4),
tetrahydrofuran (THF), n-hexane, sulfur (S.sub.8), sodium hydride
(NaH) and methanol were purchased from Aldrich Chemical Co.
.alpha.-Al.sub.2O.sub.3 (100 nm) was obtained from the Grace Derwey
Co. LTD. LiClO.sub.4 and .alpha.-Al.sub.2O.sub.3 were vacuum dried
(<10.sup.-4 torr) for 24 hours at 120.degree. C. prior to use,
and the THF was distilled under nitrogen from sodium benzophenone
before use.
[0023] B. Synthesis of Poly[Dichlorophosphazene]
[0024] Hexachlorocyclotriphosphazene, (NPCl.sub.2).sub.3, (50.0 g)
and sulfur (5.0 g), used as a catalyst, were weighed directly into
a Pyrex ampule. The ampule was evacuated to 0.05 Torr for 1 hour
and then sealed. The sealed ampule was placed in a furnace and
heated to 285.degree. C. until the melting mixture became highly
viscous but still slightly mobile. The ampule was opened, and the
contents were extracted with dry benzene to remove the cross-linked
polymer. The product, linear polymer (NPCl.sub.2)n, was then
purified by precipitation from a benzene solution into n-hexane. An
average of 50-60% conversion to the linear polymer was
obtained.
[0025] C. Synthesis of Poly[Bis(Methoxyethoxyethoxy)Phosphazene],
(MEEP)
[0026] A solution of 2-(2-methoxyethoxyethanol (64.8g, 0.54 mol)
was added to sodium hydride (13.0g, 0.54 mole) in dry THF (1000
ml). Once the sodium had reacted completely, the solution was
treated with a solution of poly(dichlorophosphazene) (25.0 g, 0.216
unit mole) in the dry THF (600 mL) under nitrogen atmosphere. The
reaction mixture was dialyzed (MWCO: 12-14000) against water (2
weeks) The residual solvent was finally removed by drying under a
vacuum to give a polymer product (36.6 g, 60% yield). Analysis of
MEEP by gel permeation chromatography (GPC) revealed a number
average molecular weight Mn=7.29.times.10.sup.4 and a
polydispersity index (PDI=Mw/Mn) of 1.44.
[0027] D. Preparation of Polymer Electrolytes
[0028] The concentration of the metal salt is expressed as the mole
ratio of the metal salt fed to a polyphosphazene repeat unit (PN),
F=[metal salt]/[PN]. In order to prepare the electrolytes,
appropriate amounts of MEEP were dissolved in a small amount of
anhydrous THF, and after the addition of the required quantity of
the corresponding metal salt, the solution was well stirred. The
composite electrolytes were obtained by dispersing the designed
amount of ceramic filler in the MEEP/metal salt solutions. The
solutions were stirred for 24 hours, and were subsequently dried in
a vacuum oven at 65.degree. C. for at least 24 hours. The dried
samples were stored in an argon-filled glovebox to avoid
contamination before measurements. Throughout this specification,
abbreviations will be used to identify the different polymer
electrolytes. In MFxAy, M represents MEEP, F represents metal salt
concentration (F2 means F=0.2), A represents ceramic filler, and y
is the wt % of the ceramic filler based on the polymer electrolyte.
The metal salt and the ceramic filler employed in the Examples are
respectively lithium perchlorate (LiClO.sub.4) and
.alpha.-Al.sub.2O.sub.3.
[0029] E. Conductivity Measurement
[0030] The ionic conductivities of the polymer electrolytes were
measured by a complex impedance method in the temperature range of
from 30 to 80.degree. C. The samples were sandwiched between
stainless steel blocking electrodes and placed in a
temperature-controlled oven at vacuum (<10.sup.-2 torr) for 2
hours before measurement. The experiments were performed in a
cylindrical cell with an electrode diameter equal to 0.785
cm.sup.2. Each electrolyte sample, which is to be measured, has a
thickness equal to 0.1 mm. The impedance measurements were carried
out on a computer-interfaced HP 4192A impedance analyzer over the
frequency range 5 Hz to 13 MHz.
[0031] F. Results
[0032] The conductivities of the polymer electrolytes prepared in
Examples 1 to 18 and Comparative Examples 1 to 6 (ceramic-free
electrolytes) are listed in Table 1.
1TABLE 1 Measured Conductivity Examples MFxAy temperature, .degree.
C. Scm.sup.-1 1 MF1A1.25 30 6.35 .times. 10.sup.-5 2 MF1A2.5 30
9.36 .times. 10.sup.-5 3 MF1A5 30 5.27 .times. 10.sup.-5 4 MF2A1.25
30 7.94 .times. 10.sup.-5 5 MF2A2.5 30 9.70 .times. 10.sup.-5 6
MF2A5 30 7.57 .times. 10.sup.-5 7 MF25A1.25 30 6.83 .times.
10.sup.-5 8 MF25A2.5 30 9.02 .times. 10.sup.-5 9 MF25A5 30 5.33
.times. 10.sup.-5 10 MF2A1.25 50 8.13 .times. 10.sup.-5 11 MF2A2.5
50 1.0 .times. 10.sup.-4 12 MF2A5 50 1.04 .times. 10.sup.-4 13
MF2A1.25 60 8.91 .times. 10.sup.-5 14 MF2A2.5 60 1.18 .times.
10.sup.-4 15 MF2A5 60 1.18 .times. 10.sup.-4 16 MF2A1.25 80 1.0
.times. 10.sup.-4 17 MF2A2.5 80 1.39 .times. 10.sup.-4 18 MF2A5 80
1.47 .times. 10.sup.-5 Comparative MF1A0 30 4.69 .times. 10.sup.-5
Example 1 Comparative MF2A0 30 6.51 .times. 10.sup.-5 Example 2
Comparative MF25A0 30 5.80 .times. 10.sup.-5 Example 3 Comparative
MF2A0 50 7.61 .times. 10.sup.-5 Example 4 Comparative MF2A0 60 8.64
.times. 10.sup.-5 Example 5 Comparative MF2A0 80 9.62 .times.
10.sup.-5 Example 6
[0033] As listed in Table 1 the conductivities of the electrolytes
measured at 30.degree. C. vary with the concentration of the
lithium salt and the amounts of the .alpha.-Al.sub.2O.sub.3 added.
The change in the conductivity is a function of the lithium salt
concentration for the MEEP/LiClO.sub.4 electrolytes with or without
.alpha.-Al.sub.2O.sub.3. For the MEEP/LiClO.sub.4 system without
.alpha.-Al.sub.2O.sub.3, the ionic conductivity initially increases
with an increasing metal salt concentration due to the increase in
the number of charge carriers, and reaches a maximum at F value of
0.2. Beyond this point, the number of ionic cross-links restricts
motion of ethyleneoxy side groups of MEEP, and fewer sites in the
right position for coordination with lithium are available to
assist the ion-pair separation, thereby reducing the ionic
conductivity. On the other hand, with the addition of
.alpha.-Al.sub.2O.sub.3, the
MEEP/LiClO.sub.4/.alpha.-Al.sub.2O.sub.3 composite electrolytes
have a higher ionic conductivity than the corresponding
MEEP/LiClO.sub.4 electrolytes. Maximum conductivities also occur at
F=0.2 for all the .alpha.-Al.sub.2O.sub.3 containing composite
polymer electrolytes. The best conductivity obtained from the one
with 2.5 wt % .alpha.-Al.sub.2O.sub.3 and F=0.2 is close to
10.sup.-4 S/cm at 30.degree. C. This is about twice that of the
pristine polymer electrolyte and is the highest value found at
ambient temperature for phosphazene polymer electrolytes. It is
also noticed that a significant conductivity enhancement of
MEEP/LiClO.sub.4 is found only over a narrow salt concentration
range (F=0.2), while the enhancement of the composite electrolyte
system with 2.5 wt % .alpha.-Al.sub.2O.sub.3 is extended over a
larger metal salt concentration region (F=0.1 to 0.25). Such
behavior may be associated with the lithium ion transport mechanism
which is closely related to the interactions among the polymer, the
lithium salt and the ceramic filler.
[0034] Besides, with the same content of lithium salt, the
conductivity of the composite electrolyte increases with increasing
.alpha.-Al.sub.2O.sub.3 content, reaches a maximum for the sample
with 2.5 wt % of .alpha.-Al.sub.2O.sub.3, and then decreases for
electrolytes with higher .alpha.-Al.sub.2O.sub.3 concentration.
This result implies that .alpha.-Al.sub.2O.sub.3plays an important
role in the ion transport mechanism in this composite polymer
electrolyte system.
[0035] Moreover, the conductivities of the composite electrolytes
with 2.5 wt % .alpha.-Al.sub.2O.sub.3 remain consistently higher
than those of the .alpha.-Al.sub.2O.sub.3-- free electrolytes in
the range of 30.degree. C.-80.degree. C.
EXAMPLES 19 to 49
[0036] A. Materials
[0037] Polyacrylonitrile (PAN, Mw: 150,000, Sp.sup.2), lithium
perchlorate (LiClO.sub.4) (Acros, reagent grade) and N,
N-dimethylformamide (DMF) were purchased from Aldrich Co. .
.alpha.-Al.sub.2O.sub.3 (100 nm) was obtained from the Grace Derwey
CO. LTD. The average particle size for TiO.sub.2 is about 5
microns. LiClO.sub.4 and .alpha.-Al.sub.2O.sub.3 were vacuum dried
(<10.sup.-3 torr) for 24 hours at 140.degree. C. prior to
use.
[0038] B. Preparation of Polymer Electrolytes
[0039] The concentration of the metal salt is expressed as the
molar ratio of the metal salt fed to a polyacryloritrile repeating
unit, F=(metal salt)/(CN). To prepare the electrolyte, an
appropriate amount of PAN was first dissolved with a small amount
of DMF. Then, the required quantity (F value) of the metal salt was
added, and the solution was stirred. A designed amount of ceramic
filler powder was then added, and the PAN/metal salt/filler
solution was stirred continuously by a high-intensity ultrasonic
finger directly immersed in the solution for 24 hours to break down
the particles. Thereafter, the solution was cast on a flat glass
and dried in a vacuum oven at a proper temperature to remove the
solvent for at least 24 hours and then taken out to cool to room
temperature. The mechanically stable membranes obtained have an
average thickness of about 100 .mu.m. The DMF residue in the
membranes estimated from TGA-IR measurement was less than 10 wt %.
The dried samples were stored in an argon-filled glovebox (water is
less than 5 ppm) to avoid moisture contamination. Throughout this
specification, abbreviations will be used to identify the different
composite polymer electrolytes. For NFxAy, N represents PAN, Fx
represents the metal salt concentration (F2 means F=0.2), A
represents the ceramic filler and y is the wt % of the ceramic
filler in the electrolyte. The metal salt employed in the Examples
is lithium perchlorate (LiClO.sub.4) The ceramic filler employed in
Examples 19-37 is .alpha.-Al.sub.2O.sub.3, and in Examples 38-49 is
TiO.sub.2.
[0040] C. Conductivity Measurement
[0041] The ionic conductivities of the polymer electrolytes were
measured by the aforesaid complex impedance method at a temperature
of 30.degree. C.
[0042] D. Results
[0043] The conductivities of the polymer electrolytes prepared in
Examples 19 to 49 are listed in Table 2.
2TABLE 2 NFxAy Measured Conductivity Examples A = .alpha. -
Al.sub.2O.sub.3 temperature, .degree. C. Scm.sup.-1 19 NF2A3.8 30
8.3 .times. 10.sup.-8 20 NF2A5 30 1.9 .times. 10.sup.-7 21 NF2A7.5
30 9.8 .times. 10.sup.-8 22 NF3A3.8 30 9.9 .times. 10.sup.-6 23
NF3A5 30 1.0 .times. 10.sup.-6 24 NF3A7.5 30 5.3 .times. 10.sup.-6
25 NF3A10 30 1.6 .times. 10.sup.-5 26 NF4A3.8 30 2.0 .times.
10.sup.-5 27 NF4A5 30 5.2 .times. 10.sup.-5 28 NF4A7.5 30 2.8
.times. 10.sup.-5 29 NF4A10 30 1.5 .times. 10.sup.-5 30 NF5A3.8 30
1.1 .times. 10.sup.-4 31 NF5A5 30 2.1 .times. 10.sup.-5 32 NF5A7.5
30 1.3 .times. 10.sup.-4 33 NFSA10 30 1.6 .times. 10.sup.-5 34
NF6A3.8 30 1.8 .times. 10.sup.-4 35 NF6A5 30 3.4 .times. 10.sup.-4
36 NF6A7.5 30 5.7 .times. 10.sup.-4 37 NF6A10 30 2.7 .times.
10.sup.-4 NFxAy Measured Conductivity Examples A = TiO.sub.2
temperature, .degree. C. Scm.sup.-1 38 NF3A3.8 30 2.8 .times.
10.sup.-6 39 NF3A5 30 5.9 .times. 10.sup.-6 40 NF3A7.5 30 1.7
.times. 10.sup.-5 41 NF4A3.8 30 2.8 .times. 10.sup.-6 42 NF4A5 30
7.3 .times. 10.sup.-5 43 NF4A7.5 30 6.0 .times. 10.sup.-5 44
NF5A3.8 30 8.6 .times. 10.sup.-5 45 NF5A5 30 2.1 .times. 10.sup.-5
46 NF5A7.5 30 1.3 .times. 10.sup.-4 47 NF6A3.8 30 7.4 .times.
10.sup.-5 48 NF6A5 30 2.7 .times. 10.sup.-4 49 NF6A7.5 30 2.4
.times. 10.sup.-4
[0044] Similar to the MEEP/LiClO.sub.4/.alpha.-Al.sub.2O.sub.3
composite electrolytes prepared in Examples 1 to 18, the
conductivities of the electrolytes PAN/LiO4/TiO.sub.2 or
.alpha.-Al.sub.2O.sub.3 prepared in Examples 19-49 measured at
30.degree. C. also vary with the concentration of the lithium salt
and the amounts of the ceramic filler added. Such conductivity
enhancement also closely relates to the extra paths of the lithium
ion transport resulted from effective Lewis acid-base interactions
among the PAN polymer, the lithium salt and the ceramic filler.
[0045] With the invention thus explained, it is apparent that
various modifications and variations can be made without departing
from the spirit of the present invention.
* * * * *